Use Navigator to drive SnackBar

Now SnackBar is an ephemeral route that uses a Placeholder to put itself into
the Scaffold.

Fixes #673

examples/fitness/lib/feed.dart

@@ -58,11 +58,9 @@ class FeedFragment extends StatefulComponent {
 }
 
 class FeedFragmentState extends State<FeedFragment> {
+  final GlobalKey<PlaceholderState> _snackBarPlaceholderKey = new GlobalKey<PlaceholderState>();
   FitnessMode _fitnessMode = FitnessMode.feed;
 
-  PerformanceStatus _snackBarStatus = PerformanceStatus.dismissed;
-  bool _isShowingSnackBar = false;
-
   void _handleFitnessModeChange(FitnessMode value) {
     setState(() {
       _fitnessMode = value;
@@ -119,15 +117,17 @@ class FeedFragmentState extends State<FeedFragment> {
     );
   }
 
-  FitnessItem _undoItem;
-
   void _handleItemDismissed(FitnessItem item) {
     config.onItemDeleted(item);
-    setState(() {
-      _undoItem = item;
-      _isShowingSnackBar = true;
-      _snackBarStatus = PerformanceStatus.forward;
-    });
+    showSnackBar(
+      navigator: config.navigator,
+      placeholderKey: _snackBarPlaceholderKey,
+      content: new Text("Item deleted."),
+      actions: [new SnackBarAction(label: "UNDO", onPressed: () {
+        config.onItemCreated(item);
+        config.navigator.pop();
+      })]
+    );
   }
 
   Widget buildChart() {
@@ -198,25 +198,6 @@ class FeedFragmentState extends State<FeedFragment> {
     }
   }
 
-  void _handleUndo() {
-    config.onItemCreated(_undoItem);
-    setState(() {
-      _undoItem = null;
-      _isShowingSnackBar = false;
-    });
-  }
-
-  Widget buildSnackBar() {
-    if (_snackBarStatus == PerformanceStatus.dismissed)
-      return null;
-    return new SnackBar(
-      showing: _isShowingSnackBar,
-      content: new Text("Item deleted."),
-      actions: [new SnackBarAction(label: "UNDO", onPressed: _handleUndo)],
-      onDismissed: () { setState(() { _snackBarStatus = PerformanceStatus.dismissed; }); }
-    );
-  }
-
   void _handleActionButtonPressed() {
     showDialog(config.navigator, (NavigatorState navigator) => new AddItemDialog(navigator)).then((routeName) {
       if (routeName != null)
@@ -240,7 +221,7 @@ class FeedFragmentState extends State<FeedFragment> {
     return new Scaffold(
       toolbar: buildToolBar(),
       body: buildBody(),
-      snackBar: buildSnackBar(),
+      snackBar: new Placeholder(key: _snackBarPlaceholderKey),
       floatingActionButton: buildFloatingActionButton()
     );
   }

examples/fitness/lib/main.dart

@@ -5,7 +5,6 @@
 library fitness;
 
 import 'package:playfair/playfair.dart' as playfair;
-import 'package:sky/animation.dart';
 import 'package:sky/material.dart';
 import 'package:sky/painting.dart';
 import 'package:sky/widgets.dart';

examples/fitness/lib/measurement.dart

@@ -112,9 +112,10 @@ class MeasurementFragment extends StatefulComponent {
 }
 
 class MeasurementFragmentState extends State<MeasurementFragment> {
+  final GlobalKey<PlaceholderState> _snackBarPlaceholderKey = new GlobalKey<PlaceholderState>();
+
   String _weight = "";
   DateTime _when = new DateTime.now();
-  String _errorMessage = null;
 
   void _handleSave() {
     double parsedWeight;
@@ -122,9 +123,11 @@ class MeasurementFragmentState extends State<MeasurementFragment> {
       parsedWeight = double.parse(_weight);
     } on FormatException catch(e) {
       print("Exception $e");
-      setState(() {
-        _errorMessage = "Save failed";
-      });
+      showSnackBar(
+        navigator: config.navigator,
+        placeholderKey: _snackBarPlaceholderKey,
+        content: new Text('Save failed')
+      );
     }
     config.onCreated(new Measurement(when: _when, weight: parsedWeight));
     config.navigator.pop();
@@ -195,18 +198,11 @@ class MeasurementFragmentState extends State<MeasurementFragment> {
     );
   }
 
-  Widget buildSnackBar() {
-    if (_errorMessage == null)
-      return null;
-    // TODO(jackson): This doesn't show up, unclear why.
-    return new SnackBar(content: new Text(_errorMessage), showing: true);
-  }
-
   Widget build(BuildContext context) {
     return new Scaffold(
       toolbar: buildToolBar(),
       body: buildBody(context),
-      snackBar: buildSnackBar()
+      snackBar: new Placeholder(key: _snackBarPlaceholderKey)
     );
   }
 }

examples/stocks/lib/main.dart

@@ -8,7 +8,6 @@ import 'dart:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
-import 'package:sky/animation.dart';
 import 'package:sky/gestures.dart';
 import 'package:sky/material.dart';
 import 'package:sky/painting.dart';

examples/stocks/lib/stock_home.dart

@@ -6,8 +6,6 @@ part of stocks;
 
 typedef void ModeUpdater(StockMode mode);
 
-const Duration _kSnackbarSlideDuration = const Duration(milliseconds: 200);
-
 class StockHome extends StatefulComponent {
   StockHome(this.navigator, this.stocks, this.symbols, this.stockMode, this.modeUpdater);
 
@@ -22,12 +20,10 @@ class StockHome extends StatefulComponent {
 
 class StockHomeState extends State<StockHome> {
 
+  final GlobalKey<PlaceholderState> _snackBarPlaceholderKey = new GlobalKey<PlaceholderState>();
   bool _isSearching = false;
   String _searchQuery;
 
-  PerformanceStatus _snackBarStatus = PerformanceStatus.dismissed;
-  bool _isSnackBarShowing = false;
-
   void _handleSearchBegin() {
     config.navigator.pushState(this, (_) {
       setState(() {
@@ -217,28 +213,18 @@ class StockHomeState extends State<StockHome> {
   }
 
   void _handleUndo() {
-    setState(() {
-      _isSnackBarShowing = false;
-    });
-  }
-
-  GlobalKey snackBarKey = new GlobalKey(label: 'snackbar');
-  Widget buildSnackBar() {
-    if (_snackBarStatus == PerformanceStatus.dismissed)
-      return null;
-    return new SnackBar(
-      showing: _isSnackBarShowing,
-      content: new Text("Stock purchased!"),
-      actions: [new SnackBarAction(label: "UNDO", onPressed: _handleUndo)],
-      onDismissed: () { setState(() { _snackBarStatus = PerformanceStatus.dismissed; }); }
-    );
+    config.navigator.pop();
   }
 
   void _handleStockPurchased() {
-    setState(() {
-      _isSnackBarShowing = true;
-      _snackBarStatus = PerformanceStatus.forward;
-    });
+    showSnackBar(
+      navigator: config.navigator,
+      placeholderKey: _snackBarPlaceholderKey,
+      content: new Text("Stock purchased!"),
+      actions: [
+        new SnackBarAction(label: "UNDO", onPressed: _handleUndo)
+      ]
+    );
   }
 
   Widget buildFloatingActionButton() {
@@ -253,7 +239,7 @@ class StockHomeState extends State<StockHome> {
     return new Scaffold(
       toolbar: _isSearching ? buildSearchBar() : buildToolBar(),
       body: buildTabNavigator(),
-      snackBar: buildSnackBar(),
+      snackBar: new Placeholder(key: _snackBarPlaceholderKey),
       floatingActionButton: buildFloatingActionButton()
     );
   }

packages/flutter/lib/src/widgets/framework.dart

@@ -50,7 +50,7 @@ typedef void GlobalKeyRemoveListener(GlobalKey key);
 /// A GlobalKey is one that must be unique across the entire application. It is
 /// used by components that need to communicate with other components across the
 /// application's element tree.
-abstract class GlobalKey extends Key {
+abstract class GlobalKey<T extends State> extends Key {
   const GlobalKey.constructor() : super.constructor(); // so that subclasses can call us, since the Key() factory constructor shadows the implicit constructor
 
   /// Constructs a LabeledGlobalKey, which is a GlobalKey with a label used for debugging.
@@ -96,9 +96,9 @@ abstract class GlobalKey extends Key {
   Element get _currentElement => _registry[this];
   BuildContext get currentContext => _currentElement;
   Widget get currentWidget => _currentElement?.widget;
-  State get currentState {
+  T get currentState {
     Element element = _currentElement;
-    if (element is StatefulComponentElement)
+    if (element is StatefulComponentElement<dynamic, T>)
       return element.state;
     return null;
   }

packages/flutter/lib/src/widgets/navigator.dart

@@ -107,10 +107,6 @@ class NavigatorState extends State<Navigator> {
 
   void pop([dynamic result]) {
     setState(() {
-      while (currentRoute.ephemeral) {
-        currentRoute.didPop(null);
-        _currentPosition -= 1;
-      }
       assert(_currentPosition > 0);
       currentRoute.didPop(result);
       _currentPosition -= 1;

packages/flutter/lib/src/widgets/placeholder.dart

@@ -0,0 +1,30 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:sky/src/widgets/basic.dart';
+import 'package:sky/src/widgets/framework.dart';
+
+class Placeholder extends StatefulComponent {
+  Placeholder({ Key key }) : super(key: key);
+
+  PlaceholderState createState() => new PlaceholderState();
+}
+
+class PlaceholderState extends State<Placeholder> {
+  Widget get child => _child;
+  Widget _child;
+  void set child(Widget child) {
+    if (_child == child)
+      return;
+    setState(() {
+      _child = child;
+    });
+  }
+
+  Widget build(BuildContext context) {
+    if (_child != null)
+      return child;
+    return new SizedBox(width: 0.0, height: 0.0);
+  }
+}

packages/flutter/lib/src/widgets/popup_menu.dart

@@ -137,7 +137,7 @@ class MenuRoute extends Route {
     return result;
   }
 
-  bool get ephemeral => false; // we could make this true, but then we'd have to use popRoute(), not pop(), in menus
+  bool get ephemeral => true;
   bool get modal => true;
   bool get opaque => false;
   Duration get transitionDuration => _kMenuDuration;

packages/flutter/lib/src/widgets/snack_bar.dart

@@ -6,21 +6,20 @@ import 'package:sky/animation.dart';
 import 'package:sky/gestures.dart';
 import 'package:sky/material.dart';
 import 'package:sky/painting.dart';
-import 'package:sky/src/widgets/animated_component.dart';
 import 'package:sky/src/widgets/basic.dart';
 import 'package:sky/src/widgets/framework.dart';
 import 'package:sky/src/widgets/gesture_detector.dart';
 import 'package:sky/src/widgets/material.dart';
+import 'package:sky/src/widgets/navigator.dart';
+import 'package:sky/src/widgets/placeholder.dart';
 import 'package:sky/src/widgets/theme.dart';
 import 'package:sky/src/widgets/transitions.dart';
 
-typedef void SnackBarDismissedCallback();
-
 const Duration _kSlideInDuration = const Duration(milliseconds: 200);
-const double kSnackHeight = 52.0;
-const double kSideMargins = 24.0;
-const double kVerticalPadding = 14.0;
-const Color kSnackBackground = const Color(0xFF323232);
+const double _kSnackHeight = 52.0;
+const double _kSideMargins = 24.0;
+const double _kVerticalPadding = 14.0;
+const Color _kSnackBackground = const Color(0xFF323232);
 
 class SnackBarAction extends StatelessComponent {
   SnackBarAction({Key key, this.label, this.onPressed }) : super(key: key) {
@@ -34,70 +33,60 @@ class SnackBarAction extends StatelessComponent {
     return new GestureDetector(
       onTap: onPressed,
       child: new Container(
-        margin: const EdgeDims.only(left: kSideMargins),
-        padding: const EdgeDims.symmetric(vertical: kVerticalPadding),
+        margin: const EdgeDims.only(left: _kSideMargins),
+        padding: const EdgeDims.symmetric(vertical: _kVerticalPadding),
         child: new Text(label)
       )
     );
   }
 }
 
-class SnackBar extends AnimatedComponent {
+class SnackBar extends StatelessComponent {
   SnackBar({
     Key key,
     this.content,
     this.actions,
-    bool showing,
-    this.onDismissed
-  }) : super(key: key, direction: showing ? AnimationDirection.forward : AnimationDirection.reverse, duration: _kSlideInDuration) {
+    this.performance
+  }) : super(key: key) {
     assert(content != null);
   }
 
   final Widget content;
   final List<SnackBarAction> actions;
-  final SnackBarDismissedCallback onDismissed;
-
-  SnackBarState createState() => new SnackBarState();
-}
-
-class SnackBarState extends AnimatedState<SnackBar> {
-  void handleDismissed() {
-    if (config.onDismissed != null)
-      config.onDismissed();
-  }
+  final PerformanceView performance;
 
   Widget build(BuildContext context) {
     List<Widget> children = [
       new Flexible(
         child: new Container(
-          margin: const EdgeDims.symmetric(vertical: kVerticalPadding),
+          margin: const EdgeDims.symmetric(vertical: _kVerticalPadding),
           child: new DefaultTextStyle(
             style: Typography.white.subhead,
-            child: config.content
+            child: content
           )
         )
       )
     ];
-    if (config.actions != null)
-      children.addAll(config.actions);
+    if (actions != null)
+      children.addAll(actions);
     return new SquashTransition(
-      performance: performance.view,
+      performance: performance,
       height: new AnimatedValue<double>(
         0.0,
-        end: kSnackHeight,
+        end: _kSnackHeight,
         curve: easeIn,
         reverseCurve: easeOut
       ),
       child: new ClipRect(
         child: new OverflowBox(
-          minHeight: kSnackHeight,
-          maxHeight: kSnackHeight,
+          minHeight: _kSnackHeight,
+          maxHeight: _kSnackHeight,
           child: new Material(
             level: 2,
-            color: kSnackBackground,
+            color: _kSnackBackground,
             type: MaterialType.canvas,
             child: new Container(
-              margin: const EdgeDims.symmetric(horizontal: kSideMargins),
+              margin: const EdgeDims.symmetric(horizontal: _kSideMargins),
               child: new DefaultTextStyle(
                 style: new TextStyle(color: Theme.of(context).accentColor),
                 child: new Row(children)
@@ -109,3 +98,28 @@ class SnackBarState extends AnimatedState<SnackBar> {
     );
   }
 }
+
+class _SnackBarRoute extends Route {
+  _SnackBarRoute({ this.content, this.actions });
+
+  final Widget content;
+  final List<SnackBarAction> actions;
+
+  bool get hasContent => false;
+  bool get ephemeral => true;
+  bool get modal => false;
+  Duration get transitionDuration => _kSlideInDuration;
+
+  Widget build(NavigatorState navigator, PerformanceView nextRoutePerformance) => null;
+}
+
+void showSnackBar({ NavigatorState navigator, GlobalKey<PlaceholderState> placeholderKey, Widget content, List<SnackBarAction> actions }) {
+  Route route = new _SnackBarRoute();
+  SnackBar snackBar = new SnackBar(
+    content: content,
+    actions: actions,
+    performance: route.performance
+  );
+  placeholderKey.currentState.child = snackBar;
+  navigator.push(route);
+}

packages/flutter/lib/widgets.dart

@@ -37,6 +37,7 @@ export 'src/widgets/material_button.dart';
 export 'src/widgets/mimic.dart';
 export 'src/widgets/mixed_viewport.dart';
 export 'src/widgets/navigator.dart';
+export 'src/widgets/placeholder.dart';
 export 'src/widgets/popup_menu.dart';
 export 'src/widgets/popup_menu_item.dart';
 export 'src/widgets/progress_indicator.dart';